1. Field of the Invention
The present invention relates to a semiconductor laser device, and more particularly to a semiconductor laser device that employs a Group III-V nitride semiconductor.
2. Discussion of the Related Art
In recent years, semiconductor lasers have been changing to smaller, more lightweight, more highly reliable, and higher output lasers, and they have been used as a light source for electronic devices such as DVD players, medical devices, and other similar devices. For these semiconductor devices, Group III-V nitride semiconductors are studied because they are capable of generating light at relatively short wavelengths.
For example, as shown in FIG. 6, a semiconductor laser includes nitride semiconductors comprising a GaN layer 21, an n-type GaN layer 22, an n-type AlGaN cladding layer 23, an n-type GaN light confinement layer 24, an active layer 25 (e.g., an InGaN multiple quantum well layer), a p-type GaN light confinement layer 26, a p-type AlGaN cladding layer 27, and a p-type GaN layer 28 onto a sapphire substrate 20 in this order. A ridge 29 is formed by etching a portion of the p-type AlGaN cladding layer 27 in the depth direction from the surface of the p-type GaN layer 28 (see, for example, Japanese Unexamined Patent Publication No. H10-256660).
In order to prevent a rise in operating voltage that causes an increase in the electrical resistance of the n-type GaN layer 22, this semiconductor laser will reduce the series resistance added to the laser device by shortening the distance between a p-type electrode 30 and an n-type electrode 31. Also, the semiconductor laser controls the excessive rise in the temperature of the devices. This allows reducing the operating voltage and increasing the reliability of the laser device.
Even if the serial resistance of the conventional semiconductor laser is reduced as described above, this semiconductor laser cannot achieve satisfactory characteristics depending on the type of semiconductor layer that has the active layer, and there are limits on the fields in which this device can be applied.
The present invention has taken the aforementioned problems into consideration, and has objects to provide a high performance and high quality semiconductor laser device that employs any type of semiconductor. In particular, the present invention employs Group III-V nitride semiconductors, which will achieve a stabilized initial laser drive impedance, and in turn an increase in the oscillation and response speeds, a reduction in noise, and the like.